III nitride epitaxial substrate, epitaxial substrate for III nitride element, and III nitride element that includes a surface nitride layer formed on the main surface of a sapphire single crystal

摘要

The crystal orientation of the main surface of a sapphire single crystal base material to constitute an epitaxial substrate is inclined from the <0001> orientation (c-axis) preferably for the <1-100> orientation (m-axis) by a range within 0.02-0.3 degrees. Then, a surface nitride layer is formed at the main surface of the base material. Then, a III nitride underfilm is formed on the main surface of the base material via the surface nitride layer. The III nitride underfilm includes at least Al element, and the full width at half maximum at (101-2) reflection in X-ray rocking curve of the III nitride underfilm is 2000 seconds. The surface roughness Ra within 5 mum area is 3.5 Å.